Anesthesia in various forms has been used in medicine for centuries. The Incas used anesthesia to allow Shamans to drill into the heads of patients to let the bad spirits escape. There have also been reported uses of anesthesia in the Far East during the 10th century to provide pain relief for birthing. Anesthesia has evolved from herbal concoctions to gas and vapor mixtures. During the 19th century, various gaseous mixtures were being used for tooth extraction by dentists. Nitrous oxide had been discovered in the late 1700's but was not used for medical purposes until the mid 1800's. Dentists also started using diethyl ether to numb their patients before performing procedures. As dentistry evolved, other types of anesthetic agents such as chloroform were discovered. The use of anesthetic agents soon spread to other practices of medicine and was being widely used in surgical procedures towards the end of the 19th century.
Inhaled anesthetic agents are unique among anesthetic drugs because they are introduced into and removed out of the body through the patient's lungs. One advantage of using inhaled anesthetics is the favorable pharmacokinetic properties (rapid onset and rapid recovery), which allow the anesthesia practitioner to quickly and effectively adjust the anesthetic depth of the patient.
In order to effectively use an inhaled anesthetic, special machines were developed to regulate the introduction of the inhaled anesthetic into the patient. One such machine is the anesthesia agent vaporizer, which is commonly referred to in the art as a “vaporizer”. Typically the vaporizer is calibrated to introduce a percentage of inhaled anesthetic agents per percentage of volume. Different types of inhaled anesthetic agents have been developed, with each of the various anesthetic agents having unique properties. In order to effectively deliver the proper amount of inhaled anesthetic agent, vaporizers are typically calibrated for a specific anesthetic agent.
Associated with the delivery of inhaled anesthetics to the patient are various alarm systems which were developed in response to specific preventable patient complications. Disconnect alarms were developed after it was realized that deaths and serious complications arose because anesthesia practitioners sometimes failed to recognize that their patients were not being ventilated. As a result oxygen sensors were introduced to prevent death and serious injuries to patients from the unrecognized administration of hypoxic or anoxic gas mixtures. Oxygen pressure alarms were also introduced after it was realized that death and other serious patient complications have arisen when there was an unrecognized loss of oxygen delivery to the anesthesia machine and thus to the patient. In each of these cases, the alarm systems are designed to bring to the attention of the practitioner a potentially harmful situation before actual injury can occur.
Recall of painful events during anesthesia and surgery is another such preventable complication. Recall of intraoperative events occurs in approximately 0.1% of all general anesthetics. Many of these patients experience devastating psychological consequences such as PTSD (post traumatic stress disorder), and painful recall is one of the leading causes for malpractice claims against anesthesiologists. Greater than 40% of all recall events are related to equipment malfunctions. These malfunctions may result from a failure to deliver anesthetic gases (agent) to the patient. One such malfunction is an empty anesthetic agent vaporizer. A majority of all such recall events are related to an undetected empty vaporizer.
On the anesthesia vaporizer, there typically exists a clear tube which reflects the amount of anesthesia agent remaining in the vaporizer. The clear tube may be difficult to see especially in low light conditions. Additionally, the anesthesia practitioner may be distracted and not paying attention to the amount of anesthetic agent reflected in the clear tube. Thus there exists a need in the industry to have an alarm system that notifies the anesthesia practitioner when the level of anesthesia agent reaches a predetermined level, allowing the anesthesia practitioner to refill or replace the vaporizer.